The present invention relates to pass band filters produced by means of linear resonators open at both their extremities, such as hairpin resonators, also referred to as U resonators, and such as the straight resonators formed by straight line sections. On this subject, it is recalled that these resonators, which are also referred to as .lambda.2 resonators, being open at both their extremities, resonate at a frequency which within the filter corresponds to a wavelength .lambda. equal to twice the electric length of the resonators. The pass band of the filter is centered on this resonance frequency.
Commonly speaking for filtration problems, and in particular for filters comprising linear resonators open at both their extremities, if it is intended to add to a pass band function a band cutout or suppressor function, for example to eliminate an undesirable frequency, a band suppressor filter is installed in series with the band pass filter. This has the disadvantage of requiring two filters and thus of requiring space and of being expensive.
The object of the present invention is to eliminate the need to utilize two filters.
This is obtained by integrating a band suppressor function within an existing band pass filter.